The present invention relates to an exhaust gas purification device of an internal combustion engine.
In the past, in a diesel engine, particulate contained in the exhaust gas has been removed by arranging a particulate filter in the engine exhaust passage, using that particulate filter to trap the particulate in the exhaust gas, and igniting and burning the particulate trapped on the particulate filter to regenerate the particulate filter. The particulate trapped on the particulate filter, however, does not ignite unless the temperature becomes a high one of at least about 600xc2x0 C. As opposed to this, the temperature of the exhaust gas of a diesel engine is normally considerably lower than 600xc2x0 C. Therefore, it is difficult to use the heat of the exhaust gas to cause the particulate trapped on the particulate filter to ignite. To use the heat of the exhaust gas to cause the particulate trapped on the particulate filter to ignite, it is necessary to lower the ignition temperature of the particulate.
It has been known in the past, however, that the ignition temperature of particulate can be reduced if carrying a catalyst on the particulate filter. Therefore, known in the art are various particulate filters carrying catalysts for reducing the ignition temperature of the particulate.
For example, Japanese Examined Patent Publication (Kokoku) No. 7-106290 discloses a particulate filter comprising a particulate filter carrying a mixture of a platinum group metal and an alkali earth metal oxide. In this particulate filter, the particulate is ignited by a relatively low temperature of about 350xc2x0 C. to 400xc2x0 C., then is continuously burned.
In a diesel engine, when the load becomes high, the temperature of the exhaust gas reaches from 350xc2x0 C. to 400xc2x0 C., therefore with the above particulate filter, it would appear at first glance that the particulate could be made to ignite and burn by the heat of the exhaust gas when the engine load becomes high. In fact, however, even if the temperature of the exhaust gas reaches from 350xc2x0 C. to 400xc2x0 C., sometimes the particulate will not ignite. Further, even if the particulate ignites, only some of the particulate will burn and a large amount of the particulate will remain unburned.
That is, when the amount of the particulate contained in the exhaust gas is small, the amount of the particulate deposited on the particulate filter is small. At this time, if the temperature of the exhaust gas reaches from 350xc2x0 C. to 400xc2x0 C., the particulate on the particulate filter ignites and then is continuously burned.
If the amount of the particulate contained in the exhaust gas becomes larger, however, before the particulate deposited on the particulate filter completely burns, other particulate will deposit on that particulate. As a result, the particulate deposits in layers on the particulate filter. If the particulate deposits in layers on the particulate filter in this way, the part of the particulate easily contacting the oxygen will be burned, but the remaining particulate hard to contact the oxygen will not burn and therefore a large amount of particulate will remain unburned. Therefore, if the amount of particulate contained in the exhaust gas becomes larger, a large amount of particulate continues to deposit on the particulate filter.
On the other hand, if a large amount of particulate is deposited on the particulate filter, the deposited particulate gradually becomes harder to ignite and burn. It probably becomes harder to burn in this way because the carbon in the particulate changes to the hard-to-burn graphite etc. while depositing. In fact, if a large amount of particulate continues to deposit on the particulate filter, the deposited particulate will not ignite at a low temperature of 350xc2x0 C. to 400xc2x0 C. A high temperature of over 600xc2x0 C. is required for causing ignition of the deposited particulate. In a diesel engine, however, the temperature of the exhaust gas usually never becomes a high temperature of over 600xc2x0 C. Therefore, if a large amount of particulate continues to deposit on the particulate filter, it is difficult to cause ignition of the deposited particulate by the heat of the exhaust gas.
On the other hand, at this time, if it were possible to make the temperature of the exhaust gas a high temperature of over 600xc2x0 C., the deposited particulate would be ignited, but another problem would occur in this case. That is, in this case, if the deposited particulate were made to ignite, it would burn while generating a luminous flame. At this time, the temperature of the particulate filter would be maintained at over 800xc2x0 C. for a long time until the deposited particulate finished being burned. If the particulate filter is exposed to a high temperature of over 800xc2x0 C. for a long time in this way, however, the particulate filter will deteriorate quickly and therefore the problem will arise of the particulate filter having to be replaced with a new filter early.
Once a large amount of particulate deposits in layers on the particulate filter in this way, a problem arises. Therefore, it is necessary to avoid the deposition of a large amount of particulate on the particulate filter. Even if avoiding the deposition of a large amount of particulate on the particulate filter in this way, however, the particulate remaining after burning will accumulate and form large masses. These masses cause the problem of clogging of the fine holes of the particulate filter. If the fine holes of the particulate filter clog in this way, the pressure loss of the flow of exhaust gas in the particulate filter gradually becomes larger. As a result, the engine output ends up falling.
An object of the present invention is to provide an exhaust gas purification device of an internal combustion engine able to separate masses of particulate causing clogging of a particulate filter from the particulate filter and discharge the same.
According to the present invention, there is provided an exhaust gas purification apparatus of an internal combustion engine in which a particulate filter for removing by oxidation particulate in an exhaust gas discharged from a combustion chamber is arranged in an engine exhaust passage and in which flow velocity instantaneous increasing means is provided for increasing the flow velocity of exhaust gas flowing through the particulate filter for just an instant in a pulse-like manner when the particulate deposited on the particulate filter should be separated from the particulate filter and discharged outside of the particulate filter.